Immersion plate heaters are used in the metal processing industry for heating solutions used to treat metal. For example, an immersion plate heater may be used to heat an acidic pickling bath used to remove the scale from steel. Because immersion plate heaters are submerged in chemical baths, they are formed of a material that should not react adversely to the chemicals of the bath. Immersion plate heaters used in the metal processing industry are made of graphite and, while they are relatively non-reactive chemically, they fracture relatively easily and threaded openings in them are susceptible to stripping.
A pressurized heated fluid such as steam is typically circulated through the immersion plate heaters to heat the bath. Fluid couplings such as nipples are used to connect the immersion plate heaters to steam lines. The connection between the fluid line and heater must provide a good seal which withstands the internal pressure of the fluid and also resists invasion of caustic chemicals from the bath solution.
A commonly used connection method is to tap threaded apertures into the heater. Reducers are threaded into the apertures to a predetermined torque. Nipples are then each threaded at one end to the reducer and connected at the other end to the steam line. Subsequent connections or disconnections between the steam line and the heater are accomplished by removing the nipples from the reducers, thereby leaving the fragile threaded engagement between the heater and reducer undisturbed. A problem with this method of connecting the fluid lines to an immersion heater is that when the nipple is rotated so as to be threaded to the reducer, it may rotate the reducer as well. The additional rotation causes an excessive torque to be applied to the threads in the fragile heater, resulting in stripping of the graphite threads, or fracturing or weakening of the graphite heater, which may cause failure once the heater is pressurized. Fractures in the immersion plate heater are particularly hazardous because failure after connection and submersion may subject an operator to pressurized spray of fluid and acidic pickling solution. Another problem is that the reducers, nipples and fluid line may be dislodged from the heat exchanger under pressure, which subjects workers to the risk of injury from these components.
An object of the present invention is to provide an improved method and apparatus for connecting fluid lines to a graphite immersion heat exchanger which prevents overtightening of reducers in the threaded aperture openings and resulting damage to the heat exchanger. Use of the present invention results in significant safety improvements, as well as increased life and performance of the heat exchanger.